Template-free synthesis of mesoporous X–Mn (X = Co, Ni, Zn) bimetal oxides and catalytic application in the room temperature removal of low-concentration NO

Abstract

Three types of Mn-based bimetal oxides (Co–Mn, Ni–Mn and Zn–Mn oxides) with well-defined mesoporosities and high specific surface areas were facilely synthesized by a template-free strategy of decomposing self-made single-phase bimetal oxalate. These bimetal oxides, featuring tunable compositions (spinel manganates) and a mesoporous structure, were applied for the first time in the room temperature catalytic removal of low-concentration (10 ppm) NO, a concerning pollutant in road tunnels and indoor parks. They demonstrated substantially enhanced efficiencies in NO removal as compared with corresponding single-metal oxides (MnO_x, Co₃O₄, NiO, ZnO), and complete conversion in up to 1.8 h at an extraordinarily high space velocity of 120 000 mL g⁻¹ h⁻¹ was achieved, which was proposed to be a result of not only the spinel manganates but also the oxygen vacancies in the amorphous Co (or Ni, Zn)-doped MnO_x framework. NO was revealed to be catalytically oxidized into NO₂ and then fixed in the bimetal oxides by forming nitrite and nitrate species.